A mercury and trace element geochemical record across Oceanic Anoxic Event 1b in Arctic Canada

A geochemical record from a continuous Arctic marine succession of the upper Aptian to upper Albian Christopher Formation exposed at Glacier Fiord on Axel Heiberg Island, Canada, reveals the characteristic carbon isotopic excursions associated with the early Albian cluster of sub-events that comprise Oceanic Anoxic Event 1b (OAE 1b). Concentrations of redox-sensitive elements in the Christopher Formation indicate that conditions ranged from oxic to anoxic, with anoxic conditions during deposition of the Kilian sub-level, and suboxic conditions during deposition of the Jacob and Paquier sub-levels of OAE 1b. Mercury is elevated above siliciclastic background at several horizons in the succession, including prior to, and following, the Jacob, Kilian, and Paquier sub-levels. Sulphides, rather than organic matter, appear to be the most important host phase for Hg in the Christopher Formation, particularly in the mid to upper Albian part of the succession following OAE 1b. A lack of enrichment of most redox sensitive trace elements, and their relationship to detrital indicators Al, Ti, and Li, combined with other indicators of overall ventilated conditions during deposition of the Christopher Formation, suggests a terrigenous source of Hg rather than fixation of Hg by S in an anoxic or euxinic setting. Although volcanic activity associated with the HALIP could have released gaseous Hg to the atmosphere and the surrounding landscape, another potential source of Hg, S, and other metal(loid)s to the basin is mineralization associated with salt diapirism that may have been exhumed by the Albian. A change in clay mineral content (K/ Al ratios) in strata overlying the Paquier sub-level indicates a change in continental weathering that may be associated with a widespread increase in humidity and warmer climate conditions at this time, that would have increased the input of detrital metal(loid)s (As, Cu, Hg, Ni, Pb, S) into the Sverdrup Basin. We suggest that Hg input into restricted marine basins can be predominantly detrital, and that there are no unequivocal atmosphericsourced Hg anomalies associated with the Jacob, Kilian, or Paquier sub-levels of OAE 1b at Glacier Fiord.

Automated summary

The geochemical record of the Christopher Formation on Axel Heiberg Island, Canada, indicates variations in redox conditions and the presence of carbon isotopic excursions associated with Oceanic Anoxic Event 1b (OAE 1b). The elevated concentrations of mercury in the formation are likely sourced from sulphide minerals rather than organic matter. The input of mercury into marine basins can be predominantly detrital, and there are no clear atmospheric sources of mercury anomalies associated with specific sub-levels of OAE 1b.